1. Field of the Invention
The field of invention relates to controlling sand production from an underground formation. More specifically, the field relates to a method for controlling loose sand particles and preventing the formation of new loose sand particles before and during production fluid production from an underground formation.
2. Description of the Related Art
During formation of the wellbore, the radial area surrounding the wellbore is exposed to high tangential stresses as the drilling operation traverses the underground formation. As the wellbore wall forms, which defines the wellbore, the high tangential stresses as the bit penetrates the underground formation pass into unconsolidated or poorly consolidated formations. Cemented sand particles are sand particles that are attached through a cementation strength to one another or to parts of the underground formation. The cementation strength between particles and a particle and the remainder of the formation can vary depending on many natural factors. Cemented sand particles are not mobile. The force that is transferred through the underground formation overcomes some of the cementation strengths, resulting in some of the cemented sand particles coming free and forming loose sand particles. The loose sand particles are operable to move about within the underground formation with the movement of the production fluid—a suspension of sand particles within the hydrocarbon and formation water or briny fluid.
A typical hydrocarbon-producing wellbore includes a production zone from which the production fluid is produced. The production fluid is conveyed to the surface through a production string. At locations along the production string, small perforations allow the produced production fluid to enter the production string from the wellbore. During production, loose sand particles enter the wellbore, into the production string through the perforations and are conveyed to the surface. Collecting sand during production of production fluid at the surface is called “sand production”, which is undesirable.
In addition to movement of loose sand particles, the flow of the hydrocarbons and water through the production zone generates a production fluid drag force. The production fluid drag force can create additional loose sand particles. The production fluid drag force increases with increasing fluid velocity of the production fluid moving through the production zone. The production fluid drag force, when sufficient, can overcome the cementation strength of a cemented sand particle, dislodging the particle from the production zone and forming a new loose sand particle. The new loose sand particles are mobile and move with the production fluid similar to the originally-formed loose sand particles. To avoid this situation, production fluid is often produced at a production rate lower than desired to prevent the inflow of new sand, which may clog downhole equipment and damage rotational surface equipment. The new loose sand particle may also damage the production zone by clogging pores close to the wellbore and preventing the flow of production fluid.
During the initiation of production, the production fluid drag force can cause severe sand production in unconsolidated or poorly consolidated sandstone hydrocarbon-bearing formations. Sand production is often triggered at the initial time of production (t=t0) as all of the loose sand particles and some of the more weekly cemented sand particles are influenced by the production fluid flowing into the wellbore. The sand production initially can be heavy if the production fluid drag force exceeds the mean cementation strength of the sand particles in the production zone as individual sand particles break free of the production zone or larger sand particle clusters disintegrate.
At the start of production from the production zone at t0, the production zone experiences the production fluid drag force for the first time. In some instances, sand production decreases with time (t>t0) as steady state at the production rate is achieved and the production fluid drag force is less than the mean cementation strength for the remaining cemented sand particles. In such an instance, new loose sand particles are not generated from the production zone. In other instances, sand production increases with time after t0. The steady state production rate produces a production fluid drag force that exceeds the mean cementation strength of the production zone. In other instances, degradation of the hydrocarbon-bearing formation due to physical erosion or chemical attack can cause the mean cementation strength of the cemented sand particles to be diminished, therefore lowering the permissible production fluid drag force without causing an increase in sand production from the production zone.
In order to limit sand from reaching the surface, various mechanical methods are employed for preventing sand produced from an underground formation from entering the production stream. Gravel packs, sand screens, standalone perforated or slotted lines and expandable sand screens are all operable to control the loose sand particles inside a wellbore; however, over time with continued sand production from the production zone the particles accumulate in the wellbore. The accumulated sand causes gradual tool failure due to erosion and increased pressure differential between the production zone and the surface, which requires additional energy to move the production fluid or downtime to permit the production zone to pressurize.
There is a need for a method of controlling the production of sand when producing from a poorly consolidated underground formation that (1) allows for longer run times, (2) does not result in increased pressure differentials, (3) does not lead to premature tool failure and (4) does not lead to additional loose sand production during production from the production zone.